Jonathan Pearlman in Kuala Lumpur and Robert Mendick

British secret services are investigating the disappearance of flight MH370, Malaysia's transport minister said on Saturday.

The disclosure that MI6 as well as the CIA are helping the Malaysian authorities will add to speculation the aircraft was hijacked by terrorists.

Hope was growing among the search teams on Saturday night that a part of the wreckage might finally have been found, three weeks after the plane vanished.

The US CIA is involved with the investigation. Photo: AFP

A photograph of an object floating in the southern Indian Ocean was taken by a Royal New Zealand Air Force plane which has been combing the seas for clues. Ships have been sent to find the object as one expert warned that it could be part of the equipment found on a shipping trawler.

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The New Zealand image followed a few hours after Chinese and Australian teams reported seeing possible debris from the plane in the same area. Until now, all possible debris has proved not to be connected to the missing passenger jet.

As the reports emerged, attention turned again to what might have caused the plane to vanish.

MI6 in London is also helping the Malaysian authorities. Photo: Reuters

Hishammuddin Hussein, Malaysia's acting transport minister, said on Saturday that MI6 and the CIA were working with Chinese spy agencies to determine what happened to the 239 passengers and crew aboard the Boeing 777. Mr Hishammuddin stopped short of plumping for one theory over any other. He said the disappearance was due to "terrorism, hijacking, personal and psychological problems, or technical failure".

"These scenarios have been discussed at length with different intelligence agencies," he said.

Crash investigators believe the disappearance of the plane and the decision to disable the communications system appear to have been deliberate. But they have found no evidence of a motive.

MI6 is understood to have helped with extensive background checks on each of the 239 passengers and crew on the plane but nothing suspicious has emerged.

Mr Hishammuddin said MI6 was also examining "pings" emitted by the plane which are being used to plot its route over the seven hours after its communications systems were disabled.

"Now that we are talking about satellite data and imagery, the CIA has been on board, Chinese intelligence has been on board, MI6 has been on board," Mr Hishammuddin said.

The Malaysia Airlines flight vanished off radar screens on its flight from Kuala Lumpur to Beijing more than three weeks ago. An explanation for its disappearance has so far proved elusive.

The plane turned wildly off course, its communications systems were "deliberately" disconnected and it carried on flying south over the Indian Ocean. It is thought to have run out of fuel and crashed into the sea off Australia.

The suggestion that intelligence agencies are involved will renew speculation that its disappearance was a criminal act, not mechanical failure.

The Malaysian police investigation has centred on MH370's pilot Zaharie Ahmad Shah. But an examination of a flight simulator seized from his home has uncovered "nothing sinister", Mr Hishammuddin said.

Zaharie, 53, a father of three and a veteran pilot, used the simulator to play games.

The different theories have done nothing to ease the anguish of families.

American lawyers acting for the family of a missing passenger believe the disappearance has been caused by some form of mechanical failure. Both Boeing and Malaysia Airlines are facing legal demands to disclose what they knew of those possible faults.

"We are working on the theory that it is a design defect," said Monica Kelly, a US attorney acting on behalf of Januarai Siregar, whose son, Firman, was on the flight.

The "Petition for Discovery", lodged in the Circuit Court of Cook County, Illinois, is intended to force both Boeing and Malaysia to release all the material they hold on the aircraft.

Until now both Boeing and Malaysia Airlines have steadfastly refused to comment on what may have caused the plane to disappear.

But details of several incidents involving other Boeing 777s have emerged, including a cockpit fire at Cairo Airport in July 2011. Although passengers and crew were moved to safety, investigators found that the blaze was caused by a short circuit igniting an oxygen pipe.

Regulators in America and Europe issued a directive ordering the replacement of the oxygen pipes. The work is estimated to cost about £1500 ($2698) to put right but last week Malaysia Airlines refused to say if the work was done.

A spokesman said: "All mandatory orders issued by aviation authorities relating to aircraft in our fleet have been complied with by Malaysia Airlines."

In the court petition, Mr Firman's lawyers, have demanded details of who designed and manufactured the oxygen system. It has also demanded Boeing release documents showing who had information "of the evidence of findings of corrosion and fractures in the fuselage of the aircraft".

The petition has also demanded Boeing provides details of who was responsible for servicing the plane.

Malaysia Airlines in turn is facing a demand to say who was responsible for training and carrying out psychological evaluations of the crew.

A Chinese surveillance plane on Friday spotted three objects - coloured white, red and orange - in a new zone west of Perth. An Australian P3 Orion spotted further items.

Though the colours of the objects appeared to match Malaysia Airlines' colours, the source of the objects has yet to be identified.

Several small objects spotted on Friday were picked up by Australian and Chinese ships and were found to be unrelated to the plane.